Genetic and Environmental Effects on Growth, Resin and Rubber Production in Guayule (Parthenium Argentatum, Gray)

by Blohm, Maren Elizabeth

Abstract (Summary)

Guayule (Parthenium argentatum Gray) is a rubber producing plant native to the
Chihuahuan Desert, which is currently being investigated as a source of hypoallergenic
latex. Current efforts are focusing on increasing latex/rubber production in the plant by
either manipulating the rubber biosynthetic pathway, altering agronomic practices to take
advantage of environmental conditions that increase rubber synthesis, or both. Field and
greenhouse studies were conducted to more fully understand the effect of genetic and
environmental manipulation on rubber production in guayule. Three guayule breeding
lines were transformed in order to increase the availability of the initiators of rubber
synthesis. The tissue-culture-derived transgenic plants and their seed-generated progeny
were grown in separate field experiments. Transformation with the genes for the
initiators of rubber synthesis did not increase rubber concentration or yield. Height and
width had high heritability estimates in the transgenic progeny and were the traits most
correlated with rubber yield, while rubber concentration was poorly correlated with
height and width. Greenhouse studies were conducted to understand why water stress
and low night temperatures increase rubber concentration. Water stress increased the
contribution of the stems to the total rubber in the plant and increased the bark to wood
ratio of the stem. Most rubber is accumulated in the stems and these two effects of water
stress contributed to the increased rubber concentration in water-stressed plants. Low
night temperature reduced plant growth without a decrease in carbon exchange.
Allocation of carbon fixation products to rubber synthesis rather than growth, contribute
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to the high rubber production under low night temperatures. Contributions from both
breeders and agronomists are needed to further improve guayule rubber/latex yield.
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